Coaches admire athletes for showing a lot of heart, and poets praise the organ’s passions, but engineers see the human cardiovascular system otherwise. The heart is a pump in a prime location, brimming with energy for the taking, says mechanical engineer Alois Pfenniger. So together with colleagues at the University of Bern and the Bern University of Applied Sciences, in Switzerland, Pfenniger has tested small turbines designed to fit inside a human artery, like an implantable hydroelectric generator.

“The heart produces around 1 or 1.5 watts of hydraulic power, and we want to take maybe one milliwatt,” Pfenniger explains. “A pacemaker only needs around 10 microwatts.” At the Microtechnologies in Medicine and Biology conference in Lucerne, Switzerland, earlier this month, Pfenniger presented results from a trial in which a tube is designed to mimic the internal thoracic artery, a millimeters-wide vessel that doctors sometimes cannibalize for surgery because it is redundant. The most efficient of the three off-the-shelf turbines he tested produced around 800 microwatts, which could run devices much more power hungry than today’s pacemakers.

Blood-pressure sensors, drug-delivery pumps, or neurostimulators could all benefit from an independent power supply. These devices are already implanted in many people, but each requires a replaceable battery or a cable to keep the power flowing. Miniaturizing such devices and eliminating cables could allow surgeons to implant them in ways that improve blood flow, reduce side effects, and add new functions. Self-contained devices could also monitor vital signs with unprecedented continuity, Pfenniger suggests.